This invention relates to organic thin film transistors having improved performance. More particularly, the invention relates to organic thin film transistors having a self-assembled monolayer between the semiconductor and gate dielectric.
Organic semiconductors are of great interest for a variety of applications centered around low-cost electronics. The view is that organics can be synthesized to incorporate the necessary electronic properties for a wide variety of devices, and also can be constructed to allow low-cost, reel-to-reel processing that is not currently possible for crystalline silicon microelectronics.
One area of concern in organic electronic devices is the quality of the interface formed between the organic semiconductor and another device layer. Much work has been done to control the nature of metal contacts to organic semiconductors using self-assembled monolayers (SAMs) and other types of xe2x80x9cdopedxe2x80x9d contacts. Previous efforts to control the semiconductor/dielectric interface have included the use of hexamethyldisilazane (HMDS) and silane coupling agents on silicon oxide surfaces. Complex deposition processes involving long times in a vacuum have been used to coat octadecyltrichlorosilane (OTS) onto thermally-grown silicon dioxide gate dielectric materials to affect transistor performance. The materials useful in this process have several disadvantages, including sensitivity to water in the atmosphere and on the surface of a dielectric layer, instability due to crosslinking within the material in competition with the bonding reaction to the dielectric layer, and difficulties in achieving reproducible film properties. EP 1041652 A2 describes the use of several surface treatments to enhance the crystalline domain size of solution cast oligothiophenes on SiOX for thin film transistors (TFTs), although measured mobility values were generally lower than the untreated controls.
The present inventors investigated organic electronic devices, and focused on the interface between the organic semiconductor and the dielectric material. They discovered materials and methods of improving the properties of organic thin film transistors. The organic thin film transistors of the invention also are suitable for manufacturing via roll-to-roll processing.
Briefly, the present invention provides a self-assembled monolayer interposed between a gate dielectric and an organic semiconductor layer, the monolayer being a product of a reaction between the gate dielectric and a precursor to the self-assembled monolayer, the precursor comprising a composition having the formula:
Xxe2x80x94Yxe2x80x94Zn,
wherein X is H or CH3;
Y is a linear or branched C5-C50 aliphatic or cyclic aliphatic connecting group, or a linear or branched C8-C50 group comprising an aromatic group and a C3-C44 aliphatic or cyclic aliphatic connecting group;
Z is selected from xe2x80x94PO3H2, xe2x80x94OPO3H2, benzotriazolyl (xe2x80x94C6H4N3), carbonyloxybenzotriazole (xe2x80x94OC(xe2x95x90O)C6H4N3), oxybenzotriazole (xe2x80x94Oxe2x80x94C6H4N3), aminobenzotriazole (xe2x80x94NHxe2x80x94C6H4N3), xe2x80x94CONHOH, xe2x80x94COOH, xe2x80x94OH, xe2x80x94SH, xe2x80x94COSH, xe2x80x94COSeH, xe2x80x94C5H4N, xe2x80x94SeH, xe2x80x94SO3H, xe2x80x94NC, xe2x80x94SiCl(CH3)2, xe2x80x94SiCl2CH3, amino, and phosphinyl;
and n is 1, 2, or 3 provided that n=1 when Z is xe2x80x94SiCl(CH3)2 or xe2x80x94SiCl2CH3.
Various thin film transistor construction options are possible. For example, the source and drain electrodes may be adjacent to the gate dielectric with the organic semiconductor layer over the source and drain electrodes, or the organic semiconductor layer may be interposed between the source and drain electrodes and the gate dielectric.
In another aspect, the present invention provides a method of making a thin film transistor comprising the steps of providing a substrate, providing a gate electrode material on the substrate, providing a gate dielectric on the gate electrode material, providing a self-assembled monolayer (SAM) adjacent to the gate dielectric, the monolayer being a product of a reaction between the gate dielectric and a precursor to the self-assembled monolayer, providing an organic semiconductor layer adjacent to the monolayer, and providing a source electrode and a drain electrode contiguous to the organic semiconductor layer. The precursor is as described above with the organic thin film transistor article. An integrated circuit comprising organic thin film transistor articles is also provided.
It is an advantage of the present invention to provide organic thin film transistors with one or more improvements over known devices that lack the features of the present invention. With the invention, improvements in properties such as threshold voltage, subthreshold slope, on/off ratio, and charge-carrier mobility can be achieved. The improvements in device performance provided by the present invention enable the production of more complicated circuits having faster switching speeds and simpler processing conditions. This invention also enables the production of larger circuit elements having comparable performance to devices with very small features. Devices with larger feature sizes can be less expensive as they do not require expensive precision patterning methods.
As used herein, xe2x80x9caxe2x80x9d or xe2x80x9canxe2x80x9d or xe2x80x9cthexe2x80x9d are used interchangeably with xe2x80x9cat least onexe2x80x9d, to mean xe2x80x9cone or morexe2x80x9d of the element being modified.
Other features and advantages of the invention will be apparent from the following detailed description of the invention and the claims. The above summary of principles of the disclosure is not intended to describe each illustrated embodiment or every implementation of the present disclosure. The figures and the detailed description that follow more particularly exemplify certain preferred embodiments utilizing the principles disclosed herein.